The last time I saw the Yukon, a 366-foot-long Canadian navy destroyer, it was docked in San Diego. So many holes had been cut in the sides of this well-worn vessel that it reminded me of a big hunk of Swiss cheese.

That was a little more than a decade ago, and volunteer crews were gutting and cleaning the ship, preparing to scuttle it to create an artificial reef in 105 feet of water two miles off Mission Bay.

Since then, I've wanted to visit the ship in its sandy resting spot, but the birth of two children and a move to Wisconsin got in the way.

Now I was floating on the Humboldt dive boat, listening to captain Ryan Wilbarger as he briefed us about what we would find on the ship. He also warned us, in no uncertain terms, not to enter the Yukon unless we had training in technical diving.

Then, warm and toasty in a thick wetsuit to ward off the chill of 50-degree water we would find in the depths, I jumped in. Several feet away floated Virginia Hatter, a scuba instructor and my guide for a day of diving on the Yukon and the nearby Ruby E, a 165-foot Coast Guard cutter sunk in 1989 in about 90 feet of water. The ships are two of six vessels that make up San Diego's "Wreck Alley," about two miles off the coast and one of the area's premier dive spots.

Because I hadn't dived in more than a year — and because the Yukon is a challenging outing in potentially strong currents — I'd warmed up the day before with a relatively shallow dive. I chose the cove at the southern end of La Jolla Ecological Reserve to check out the kelp and look for sevengill sharks with instructor Nick Le Beouf, who works for the OEX dive and kayak shop in La Jolla.

We weren't disappointed in our search for the sevengills. During our 45-minute meander, we encountered five of them, including one that was close enough for LeBeouf to touch.

Though we also saw bright orange garibaldis (which look like giant goldfish), crabs, starfish, lobster and a variety of fish, the best part was swimming through the translucent kelp, which waved each time the ocean surged.

We spent most of our time in the cove, where I had dived a decade ago, at less than 40 feet, so I was still a bit nervous the next day when it came time to descend 100 feet to the Yukon.

"A little nervousness is good," Hatter had told me on the Humboldt deck as we checked out our gear and made sure we had plenty of air. "You never want to be cocky about diving."

At a buoy marking the bright gold line that descended to the deck of the Yukon, Hatter gave me an energetic OK sign (the thumb and forefinger in a circle) as we simultaneously let the air out of our buoyancy compensation vests and began to drop.

I cleared my ears repeatedly as I slid slowly down the line, keeping my eye on the blinking strobe light she had clipped to her vest. Visibility was about 25 feet that day, but the water became green and dark the deeper we dropped and — truth be told — a little creepy.

After we descended for several minutes, the outlines of the ship's superstructure came into view, then the bow, a ladder, a round window and gun turrets. One of the first things I noticed when I got up close were foot-tall, flower-like white giant plumose anemones that were blooming all over the Yukon.

On closer inspection, I could also see that a carpet of red, pink, purple-orange and red club-tipped anemones covered the hull. A brilliant blue and gold nudibranch stood out from the other, more subtle colors. Over the last decade, the Yukon had changed from a rusting hulk into an undersea garden, thanks to cold, nutrient-rich currents.

Because the ship tipped on its port side when it sank, the deck had become a 40-foot wall, with its towers and gear facing west. As we swam along the 90-degree deck, we saw sheepshead, rockfish, cabazon, goby, blacksmith, surfperch and a large crab hiding in a ladder.

On another spot, wavy kelp slurped in and out of a hole in the deck with the gentle surge. When it is stronger, I was warned, divers can be sucked into the hull and then spit out.

After 20 minutes, we began a slow ascent, pausing several times for safety stops to let nitrogen bubbles escape our blood. Back on board the Humboldt, we warmed up with hot tea, soup and salad.

An hour later, we were back on the Yukon. I poked my head inside the hull and was tempted to enter. But caution — and fear of a scolding — kept me outside. Then we swam forward to check out the gun turrets and big cutouts in the shape of dolphins in the bow.

For the last dive of the day, we descended to the Ruby E, which is beginning to crumble after nearly 25 years underwater. To my eye, it was more colorful and heavily forested with anemones and other sea critters than the Yukon was.

Better yet, it had a more interesting story than that of the Yukon, which was launched in 1961 and had a relatively uneventful career. The Ruby E, however, was built in Seattle during Prohibition and designed to catch rumrunners bringing in hooch from Canada.

It patrolled Alaskan waters for submarines during World War II, was decommissioned in 1950 and ended its career, so the stories go, running drugs from Mexico to California.

Waterhorse Charters, 1617 Quivira Road, San Diego; (619) 224-6195, http://www.waterhorsecharters.com, offers dives on the Yukon, the Ruby E and other ships in San Diego's Wreck Alley. A typical three-tank outing on its Humboldt dive boat costs $104 and includes air fills, tanks, food and beverages....